Magnetic coupling in trinuclear partial cubane copper(II) complexes with a hydroxo bridging core and peripheral phenoxo bridges from NNO donor Schiff base ligands

Three new trinuclear copper(II) complexes, [(CuL¹)₃(μ₃-OH)](ClO₄)₂·3.75H₂O (1), [(CuL²)₃(μ₃-OH)](ClO₄)₂(2) and [(CuL³)₃(μ₃-OH)](BF₄)₂·0.5CH₃CN (3) have been synthesized from three tridentate Schiff bases HL¹, HL², and HL³ (HL¹ = 2-[(2-amino-ethylimino)-methyl]-phenol, HL² = 2-[(2-methylamino-ethylimino)-methyl]-phenol and HL³ = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol). The complexes are characterized by single-crystal X-ray diffraction analyses, IR, UV-vis and EPR spectroscopy, and variable-temperature magnetic measurements. All the compounds contain a partial cubane [Cu₃O₄] core consisting of the trinuclear unit [(CuL)₃(μ₃-OH)]²⁺ together with perchlorate or fluoroborate anions. In each of the complexes, the three copper atoms are five-coordinated with a distorted square-pyramidal geometry except in complex 1, in which one of the Cu^II ions of the trinuclear unit is six-coordinate being in addition weakly coordinated to one of the perchlorate anions. Variable-temperature magnetic measurements and EPR spectra indicate an antiferromagnetic exchange coupling between the Cu^II ions of complexes 1 and 2, while this turned out to be ferromagnetic for complex 3. Experimental values have been fitted according to an isotropic exchange Hamiltonian. Calculations based on Density Functional Theory have also been performed in order to estimate the exchange coupling constants in these three complexes. Both sets of values indicate similar trends and specially calculated J values establish a magneto-structural correlation between them and the Cu-O-Cu bond angle, in that the coupling is more ferromagnetic for smaller bond angle values.     

From “naked” copper(II) ions and asymmetric macrocyclic complex linkers with a monodentate top and a bidentate top to molecular rectangle and infinite molecular rectangle strands

A molecular rectangle [Cu{CuL¹(NO₃)}(H₂O)(NO₃)]₂ (1) and two infinite molecular rectangle strands {[Cu{CuL¹(NO₃)}₂] · 2H₂O}_∞ (2) and [Cu{CuL²(ClO₄)}₂]_∞ (3) were prepared by reaction of “naked” Cu(II) ions with macrocyclic complex ligands CuL¹ for 1 and 2 and CuL² for 3 in metal-to-ligand molar ratios of 1:1, 1:2 and 1:2, respectively. L¹ and L² denote the dianions of diethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate and diethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively. The structures of 1-3 were determined by X-ray single-crystal analyses. CuL¹ in 1 and 2 and CuL² in 3 act as angular linkers with a monodentate coordination top and a bidentate one between two Cu(II) nodes to enclose the molecular rectangle of 1 and the rectangular subunits of 2 and 3. The angular shape, the monodentate top plus bidentate top coordination mode and the self-complementarity for π?π interactions of the macrocyclic complex linkers, the ratio between the reactants and the octahedral coordination geometry of the naked Cu(II) ions jointly determined the interesting structures of metallocyclophane 1 and 1D double chain coordination polymers 2 and 3. The cavities of the rectangular molecules of 1 are arranged into infinite strands so that parallel channels occur in the crystal. The molecules of 2 and 3 all pack parallel in the crystals.     

Syntheses, crystal structures and magnetic properties of trinuclear and [3 × 1 + 1 × 2] pentanuclear complexes derived from a compartmental ligand: Role of solvent on nuclearity and number of components

Reaction of [Cu^IIL⊂(H₂O)] (H₂L = N,N′-ethylenebis(3-ethoxysalicylaldimine)) with nickel(II) perchlorate in 1:1 ratio in acetone produces the trinuclear compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂ (1). On the other hand, on changing the solvent from acetone to methanol, reaction of the same reactants in same ratio produces the pentametallic compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)]·2MeOH (2A), which loses solvated methanol molecules immediately after its isolation to form [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)] (2B). Clearly, formation of 1 versus 2A and 2B is solvent dependent. Crystal structures of 1 and 2A have been determined. Interestingly, compound 2A is a [3 × 1 + 1 × 2] cocrystal. The cryomagnetic profiles of 1 and 2B indicate that the two pairs of copper(II)···nickel(II) ions in the trinuclear cores in both the complexes are coupled by almost identical moderate antiferromagnetic interaction (J = −22.8 cm⁻¹ for 1 and −26.0 cm⁻¹ for 2B).     

Making 3d-4f hexanuclear clusters from heterotrinuclear cationic building blocks

The syntheses and crystal structures of two new hexanuclear complexes are reported: [{(LCu^II(ONO₂))(LCu^II(H₂O))Nd^III}₂(μ-C₂O₄)](NO₃)₂ · 6H₂O (1) and [{(LNi^II(H₂O))(N(CN)₂)}₂Pr^III}₂(ONO₂)](OH) · 2H₂O · 3CH₃CN (2) (L is the dianion of the Schiff-base resulted from the 2:1 condensation of 3-methoxysalyciladehyde with 1,3-propanediamine). Compounds 1 and 2 were obtained by connecting heterotrinuclear cationic complexes [{LM^II}₂Ln^III]³⁺ with oxalato or nitrato linkers. The structure of the complex cation in 1 shows two almost linear trinuclear [Cu₂Nd] moieties which are linked by a bis-chelating oxalato bridge between the neodymium ions. The hexanuclear cationic moiety in 2 is built up of two heterotrinuclear [Ni₂Pr] units that are linked by a nitrato group bridging two praseodymium(III) ions. The spectroscopic (FTIR, UV-Vis) and magnetic properties of 1 and 2 have been investigated.     

Carbonyl compound dependent hydrolysis of mono-condensed Schiff bases: A trinuclear Schiff base complex and a mononuclear mixed-ligand ternary complex of copper(II)

Two Schiff bases, HL¹ and HL² have been prepared by the condensation of N-methyl-1,3-propanediamine (mpn) with salicylaldehyde and 1-benzoylacetone (Hbn) respectively. HL¹ on reaction with Cu(ClO₄)₂·6H₂O in methanol produced a trinuclear Cu^II complex, [(CuL¹)₃(μ₃-OH)](ClO₄)₂·H₂O·0.5CH₂Cl₂ (1) but HL² underwent hydrolysis under similar reaction conditions to result in a ternary Cu^II complex, [Cu(bn)(mpn)ClO₄]. Both complexes have been characterised by single-crystal X-ray analyses, IR and UV-Vis spectroscopy and electrochemical studies. The partial cubane core [Cu₃O₄] of 1 consists of a central μ₃-OH and three peripheral phenoxo bridges from the Schiff base. All three copper atoms of the trinuclear unit are five-coordinate with a distorted square-pyramidal geometry. The ternary complex 2 is mononuclear with the square-pyramidal Cu^II coordinated by a chelating bidentate diamine (mpn) and a benzoylacetonate (bn) moiety in the equatorial plane and one of the oxygen atoms of perchlorate in an axial position. The results show that the Schiff base (HL²) derived from 1-benzoylacetone is more prone to hydrolysis than that from salicylaldehyde (HL¹). Magnetic measurements of 1 have been performed in the 1.8-300 K temperature range. The experimental data clearly indicate antiferromagnetism in the complex. The best-fit parameters for complex 1 are g = 2.18(1) and J = −15.4(2) cm⁻¹.     

Two Hg(II) complexes with a capped trigonal prismatic geometry derived from multidentate macrocyclic ligands containing N and S donors, with coordinated anions

Two Hg(II) complexes [HgL′(ClO₄)₂] (1) and [HgL(ClO₄)]ClO₄ (2) derived from the macrocyclic ligands, 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane (L′) and 7-(pyridin-2-ylmethyl)-1,4,10-trithia-7,13-diazacyclopentadecane (L), have been crystallographically characterised. Ligand L and its Hg(II) complex were isolated unexpectedly, and a possible formation pathway of the ligand is proposed. By including weakly bound O atoms from the perchlorate ions, the Hg atoms in both complexes are seven-coordinate and possess capped trigonal prismatic geometries. These uncommon structures for Hg(II) complexes were achieved mainly by the relatively large size of the metal ion and the steric effect from the macrocycles. In both complexes, strong hydrogen bonding between the amine hydrogen atom and a perchlorate ion was observed. For complex 1, the interaction is N(3)-H(15)···O(8) at 2.08(12) Å where O(8) is of the same anion as one of the coordinated O atoms; in complex 2, a similar hydrogen bond, N(7)-H(7)···O(32), with a distance of 2.25 Å, is formed to the coordinated anion, but the second anion remains discrete.     

Coordination polymers of Cu(II) and Cd(II) with bifunctional chelates of the type dipicolylamino-alkylcarboxylate, (NC5H4CH2)2N(CH2)nCO2H (n = 1, 2, 3 and 4)

A series of bifunctional chelates of the type dipicolylamino-alkylcarboxylate (NC₅H₄CH₂)₂N(CH₂)_nCO₂H (n = 1-4; HL¹-HL⁴, respectively) has been prepared. Reactions of the ligands in aqueous methanol/N,N-dimethylformamide with the appropriate Cu(II) salts yielded the compounds [CuL¹](NO₃)·H₂O (1·H₂O), [CuL²(H₂O)]BF₄·H₂O (2·H₂O), [Cu(HL³)(SO₄)]₂ (3) and [CuL⁴(NO₃)]·MeOH (4·MeOH). While compounds 1, 2 and 4 are one-dimensional, the detailed connectivities within the chains are quite distinct, depending on factors such as alkyl chain length and ligation of aqua ligands or anionic components. In contrast to 1, 2 and 4, the structure of 3 is molecular, a binuclear assembly of edge-sharing Cu(II) ‘4+2’ distorted octahedra. The Cd(II) species, [{CdL²}₂(SO₄)]·4H₂O (5·4H₂O), prepared from HL² and CdSO₄·nH₂O in aqueous methanol/N,N-dimethylformamide, is two-dimensional, with a network constructed from binuclear units of seven coordinate Cd(II), , linked through bridging SO₄²⁻ groups to produce an assembly of linked hexagonal rings [{CdL²}₂(SO₄)]₆.     

Use of acid-base and redox chemistry to synthesize cobalt(III) and iron(III) complexes of a partially deprotonated triprotic imidazole-containing Schiff base ligand: Hydrogen bound 1D linear homochiral and zig-zag heterochiral supramolecular complexes

Aerial reaction of cobalt(II) perchlorate with H₃(1) [H₃(1) is the tripodal ligand derived from the condensation of tris(2-aminoethyl)amine with three equivalents of imidazole-2-carboxaldehyde] in methanol and [FeH₃(1)(ClO₄)₂] with Fe(1) in acetonitrile results in the formation of [CoH₂L](ClO₄)₂·H₂O and [FeHL]ClO₄·CH₃CN, respectively. Mössbauer spectroscopy and variable temperature magnetic susceptibility indicate that [FeHL]ClO₄·CH₃CN is a low spin iron(III) species. Both complexes were characterized by EA, IR, and single crystal structure determinations. Both complexes crystallize in the centrosymmetric monoclinic space group, P2₁/c, so both enantiomers of the chiral complex are present. The supramolecular features of these complexes, caused by the partial deprotonation of the ligand and the resultant formation of imidazole-H···imidazolate hydrogen bonds, are different. [FeHL]⁺ forms hydrogen bonds with molecules from adjacent cells of like chirality. This results in a linear homochiral array of iron complexes. In contrast, [CoH₂L]²⁺ forms hydrogen bonds with a molecule from the same cell and one from another cell resulting in an 1D alternating heterochiral zig-zag chain.     

Synthesis, crystal structure and magnetic properties of cubane and linear trinuclear nickel complexes formed by 3,5-dichloro-2-hydroxybenzylaminoacetic acid

The reaction of Ni(ClO₄)₂·6H₂O with 3,5-dichloro-2-hydroxy-benzylaminoacetic acid (H₂dchaa), NaN₃ and triethylamine in methanol solution or water solution under solvothermal methods leads to the formation of two completely different Ni^II compounds: [HN(C₂H₅)₃]₈·[Ni₄(dchaa)₄(N₃)₄]₂ (1) and [HN(C₂H₅)₃]₂·[Ni₃(dchaa)₄(H₂O)₄]₂·(H₂O)₂ (2). The complexes 1 and 2 have been characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction. Structure analyses reveal that complex 1 is a cubane cluster, while the complex 2 is a linear trinuclear cluster. The magnetic investigation shows that complexes 1 and 2 exhibit a ferromagnetic coupling between Ni^II ions. Ac susceptibilities of 1 and 2 reveal no frequency-dependent out-of-phase signals and the corresponding magnetic properties were discussed.     

Angular trinuclear copper(II) complexes of N4O-donor ligand: Syntheses, crystal structures and magnetic properties

Two trinuclear copper(II) complexes of a Schiff-base type N₄O-donor ligand (LH) derived from 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione and 1,3-diaminopropan-2-ol are reported. Complex [Cu₃L₂(ClO₄)₄] (1) has an angular C₂-symmetric trinuclear core as revealed from single-crystal X-ray diffraction studies. The terminal coppers are in square-pyramidal geometry with an N₃O₂ coordination environment while the central one is in octahedral geometry with an N₂O₄ donor environment. Complex [Cu₃L₂(ClO₄)(N₃)(H₂O)](ClO₄)₂ · H₂O (2) has an unsymmetrical trinuclear core with an intramolecular hydrogen bonding interaction between the water and azide anion coordinated to Cu(1) and Cu(3) center, respectively. All the copper centers in 2 are in square-pyramidal geometry. The average Cu?Cu distance between closest metal ions in both the complexes is 3.897 Å. The coordination environment of coppers in 1 approximately mimics that of multicopper oxidases in the oxidized form and the environment in 2 mimics that of the azide derivative of ascorbate oxidase. Both 1 and 2 exhibit doublet spin ground state due to strong antiferromagnetic coupling operating through the alkoxo-bridged oxygen atoms between the copper centers.     

Preparation, structures and properties of dinuclear and trinuclear copper(II) complexes bridged by one oximato and one hydroxo ligands

The dinuclear and trinuclear copper(II) complexes [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ · [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1) and [Cu₃(L)₂(OH)₂(H₂O)₂](NO₃)₂ (2) (HL=2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime and phen=1,10-phenanthroline) were prepared and their crystal structures have been determined by X-ray crystallography. Complex 1 is composed of [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ (1a) and [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1b). In 1a and 1b, one oximato of L and one hydroxo group bridge two copper(II) ions. The linear trinuclear cation [Cu₃(L)₂(OH)₂(H₂O)₂]²⁺ in 2 is centrosymmetric, and one oximato and one hydroxo group bridge the central and terminal copper(II) ions. The strong antiferromagnetic interactions within the dinuclear and trinuclear complexes 1 and 2 have been observed (2J=∼−900 cm⁻¹ for 1 and 2, respectively, H=−2JS₁·S₂).     

Gold(I) and silver(I) complexes of 2,3-bis(diphenylphosphino)maleic acid: Structural studies and antitumour activity

The 2:1 and 1:2 adducts of Au(I) and 1:2 adducts of Ag(I) with the diphosphine 2,3-bis(diphenylphosphino)maleic acid (dpmaa) have been prepared in high yields. Crystal structures have been determined for the neutral digold complex (AuCl)₂(dpmaa) · 2thf (1) and the bis-chelated complex [Au(dpmaa)₂]Cl · H₂O · CH₃OH (2). For 1, conformational rigidity imposed by the ethylenic bridge facilitates the formation of short intramolecular Au-Au contacts with no evidence of similar intermolecular contacts. Complex 2 crystallizes with [Au(dpmaa)₂]⁺ cations hydrogen bonded through the carboxyl groups to a water molecule and chloride anion to form a H-bonded chain along the a axis. ³¹P NMR titration of 1 with dpmaa in acetone shows conversion to 2 at Au:P-P ratios less than 1:1 indicating similar high thermodynamic and kinetic stabilities to other bis-chelated [Au(P-P)₂]⁺ complexes containing 5- or 6-membered chelate rings. The ionic Au(I) complex 2 and the analogous Ag(I) complex [Ag(dpmma)₂]NO₃ (3) are highly water soluble. The in vitro cytotoxic activity of 2 was assessed against eight different cell lines and no significant activity was found. The solubility properties and solution behaviour of the complexes are compared to the analogous 1,2-bis(diphenylphosphino)ethane (dppe) complexes and the potential significance of these results to the antitumour properties of chelated 1:2 Au(I)diphosphine complexes are discussed.     

Synthesis, characterization and bioactivity of two novel trinuclear Cu(II)/Ni(II) complexes with pentadentate ligand N-2-methyl-acryloyl-salicylhydrazide

Two new trinuclear complexes, Cu₃L₂(py)₂ (1) and Ni₃L₂(py)₄ (2), have been synthesized and characterized, where L³⁻ is N-2-methyl-acryloyl-salicylhydrazidate. Central metal ion and two terminal metal ions in the two complexes are combined by two bridging deprotonated L³⁻ ligands, forming a bent trinuclear structure unit with an M-N-N-M-N-N-M core. The bent angles in complexes 1 and 2 are 167.6(1)° and 75.4(1)°, respectively. Three nickel ions in compound 2 exhibit alternating square-planar and octahedral geometries, while three copper ions in compound 1 follow square-planar mode. The studies in solution integrity and stability of compounds 1 and 2 show they are soluble and stable in DMF. UV-Vis titrations demonstrate compound 1 is stable in DMF even in the presence of excess metal ions. Antibacterial screening data indicate the two compounds all have stronger antimicrobial activities against the tested microorganisms than ligand. The trinuclear copper compound 1 is more active than monocopper compounds in the previous study, and the trinuclear nickel compound 2 is less active than tetranuclear nickel compound in the previous study.     

Sterically-controlled nuclearity in new copper(II) complexes with di-compartmental ligands: Formation of antiferromagnetically coupled angular trimer and mononuclear inclusion complex

Two new copper(II) complexes, [Cu₃(L¹)₂(H₂O)₂](ClO₄)₂ (1) and [CuL²⊂ (H₂O)] (2) have been derived from two di-compartmental Schiff base ligands H₂L¹ and H₂L², respectively. Depending on slight modification of the substituent group of the potentially N₂O₄ donor ligands, tri- and mononuclear structures are obtained, which have been confirmed by single-crystal X-ray diffraction studies. Both complexes have been characterized by elemental analysis, IR, UV-vis and EPR spectroscopy. Complex 1 consists of an angular trinuclear array of copper ions, while complex 2 consists of a mononuclear copper center. Variable temperature magnetic susceptibility measurements have been performed to investigate the magnetic behaviour of complex 1 and the result indicates a strong antiferromagnetic exchange interaction (J = −120.1(2) cm⁻¹) between the adjacent copper(II) centers through two double μ₂-phenoxo bridges. Complex 2 is a mononuclear inclusion compound encapsulating one water molecule in the vacant external compartment of the ligand through hydrogen-bonding interactions.     

New supramolecular complexes generated from Mn, Fe, Co, Zn, Fe with a bent dipyridyl ligand: Metal- and anion-directed assembly

Assemblies of an angular dipyridyl ligand 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo) with a series of metal perchlorate afford five new supramolecular complexes with the general formula of [M(4-bpo)₂(H₂O)₄] · (4-bpo)₂ · (anion) · (solvent), in which M = Mn^II for 1, Fe^II for 2, Co^II for 3, Zn^II for 4, and Fe^III for 5. Although similar molecular structures and compositions are found for these mononuclear complexes, they display two types of supramolecular lattices. Complexes 1, 4 and 5 similarly crystallize in space group P2/n or P2/c. The complex cations, free 4-bpo and lattice water are linked to generate 2D layered frameworks with the aid of hydrogen bonding, and the counter anions are located within and between (also methanol in 5) these 2D arrays. However, complexes 2 and 3 are isostructural in space group . Two types of alternate 2D layers consisting of complex cations and free 4-bpo components, respectively, are observed with the anions and lattice water locating between them. These motifs are interlinked by complicated hydrogen-bonding to form a 3D intercalated network. Moreover, when Co(NO₃)₂ is used instead of Co(ClO₄)₂ in the assembly of 3, a 1D polymeric chain complex {[Co(4-bpo)(H₂O)₂(NO₃)₂](H₂O)₃}_n (6) is generated. These results indicate that the choice of metal ion and anion exerts a significant influence on governing the target complexes. A comparison of the structural features for all metal perchlorate complexes with 4-bpo is also briefly discussed.     

Synthesis, spectroscopic properties, X-ray single crystal analysis and antimicrobial activities of organotin(IV) 4-(4-methoxyphenyl)piperazine-1-carbodithioates

A series of mononuclear organotin(IV) complexes of the types, R₃SnL {R = C₄H₉ (1), C₆H₁₁ (2), CH₃ (3) and C₆H₅ (4)}, R₂SnClL {R = C₄H₉ (5), C₂H₅ (7) and CH₃ (9)} and R₂SnL₂ {R = C₄H₉ (6), C₂H₅ (8) and CH₃ (10)}, have been synthesized, where L = 4-(4-methoxyphenyl)piperazine-1-carbodithioate. The ligand-salt and the complexes have been characterized by Raman, FT-IR and multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy and elemental microanalysis (CHNS). The spectroscopic data substantiate coordination of the ligands to the organotin moieties. The structures of complexes 4 and 6 have been determined by single-crystal X-ray diffraction and illustrate the asymmetric bidentate bonding of the ligand. The packing diagrams indicate O···H and π···H intermolecular interactions in complex 4 and intermolecular S₂C···H interactions in complex 6, resulting in layer structures for both complexes. A subsequent antimicrobial study indicates that the compounds are active biologically and may well be the basis for a new class of fungicides.     

Extended molecular networks based on Zn and Cd imparting N-substituted imidazole

Synthesis of complexes with the formulations [M(CPI)₂Cl₂] (M = Zn, 1; M = Cd, 4) and [M(CPI)₆](X)₂ (M = Zn, X = NO₃⁻, 2; X = ClO₄⁻, 3; M = Cd, X = NO₃⁻, 5; X = ClO₄⁻, 6) have been achieved from the reactions of MCl₂, M(NO₃)₂·xH₂O and M(ClO₄)₂·xH₂O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, ¹H, ¹³C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature.     

Synthesis, characterization and magnetic properties of new homotrinuclear copper(II) complexes

Two new mononuclear bis(oxamato) complexes with the formula [nBu₄N]₂[M(nabo)] M = Ni (4), Cu (5), with nabo = 2,3-naphthalene-bis(oxamato) have been synthesized as precursors for trinuclear oxamato-bridged transition metal complexes. Starting from 5 the homo-trinuclear complex [Cu₃(nabo)(pmdta)₂(BF₄)](BF₄) · MeCN · Et₂O (7), with pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, has been prepared. The central N,N′-2,3-naphthalene bridge of 7 is so far the most extended π-conjugated bridge of trinuclear bis(oxamato) type transition metal complexes. The goal of this work was to verify the N,N′-2,3-naphthalene bridge of 7 on its magnetic properties in comparison to the N,N′-o-phenylene bridge of the related homo-trinuclear complex [Cu₃(opba)(pmdta)₂(NO₃)](NO₃) · 2MeCN (6) (opba = o-phenylene-bis(oxamato)). The crystal structures of 4-7 were solved. The magnetic properties of 6 and 7 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, values of −89 cm⁻¹ (6) and −113 cm⁻¹ (7) were obtained. The different J values are discussed based on the crystal structures of 6 and 7.     

Structure and magnetism of two new linear trinuclear copper(II) clusters obtained from the tetradentate N2O2 ligand bis(2-hydroxybenzyl)-1,3-diaminopropane

Reaction of bis(2-hydroxybenzyl)-1,3-diaminopropane (H₂bhbd) with copper(II) perchlorate and copper(II) chloride in methanol, respectively, leads to linear trinuclear clusters, namely [Cu₃(bhbd)₂(CH₃OH)₂(ClO₄)₂] (1) and [Cu₃(bhbd)₂Cl₂](CH₃OH)₄ (2). These coordination compounds were characterized by X-ray crystallography, UV-Vis, IR and EPR spectroscopy, and magnetic susceptibility measurements. Both complexes have a linear trinuclear array of copper ions bridged by means of phenolato O atoms and separated by a distance of 2.985(4) Å (1) and 2.937(4) Å (2). Strong antiferromagnetic interactions between these adjacent Cu^II ions govern the magnetochemistry of 1 (J = −303(1) cm⁻¹) and 2 (J = −482(3) cm⁻¹) resulting in S = 1/2 ground states fully populated below 150 K. A correlation between the interaction parameter J and the angles within the trinuclear clusters is proposed.     

Transition metal complexes based on pyridine ligand containing both bis(2-pyridyl) and 1,3-dithiole-2-ylidene units: Syntheses, structures, and magnetic studies

Two new mononuclear spin-crossover iron(II) complexes, [FeL₂(NCS)₂] · H₂O (1) and [FeL₂(NCSe)₂] (2), have been synthesized from the reaction of the versatile ligand 4,5-bis(2-cyanoethylthio)-2-bis(2-pyridyl)methylene-1,3-dithiole (L), Fe(ClO₄)₂, and KNCX (X = S/Se). Reactions of L with Cu^II or Co^II salts afford one mononuclear complex [CuL(hfac)₂] · CH₃OH (hfac = hexafluoroacetylacetonate) (3), one dinuclear complex [(CuLCl)₂(μ-Cl)₂] · CH₃OH (4), and two 1D chain species, [CuL₂]_n(BF₄)_2n (5) and [CoL₂]_n(ClO₄)_2n · 2nCH₂Cl₂ (6). The crystal structures of complexes 1 and 3-6 have been determined by X-ray crystallography. Short intermolecular S?S contacts between neighboring 1D arrays are observed in 5 and 6, which lead to the formation of the 2D structure. The magnetic properties are studied, and antiferromagnetic couplings between the Cu^II centers across the chloride bridges have been found in 4 (J = 2.04 cm^-1). Spin-crossover behaviors between high and low spin states are observed at T_1/2 = 80 K for 1 and T_1/2 = 300 K for 2, respectively.